The present invention relates to a head gimbal assembly (HGA) for use in a magnetic information storage disk drive. In particular, the present invention relates to a HGA design having superior performance during track accessing.
FIG. 1 illustrates a conventional hard disk drive design. Hard disk drives are used as the major storage unit in a computer. Hard disk drives operate by storing and retrieving digitized information onto and from a rotating disk. The reading and writing of the information onto the disk is performed by a magnetic “head” embedded in a ceramic “slider” which is mounted on a piece of a metal spring, called a suspension. The suspension consists of many components, such as a load beam, a gimbal, traces, a hinge and a base plate. The suspension provides two functions: mechanical support and electrical connection between the “head” and the “pre-amplifier.” The slider flies on the rotating disk with about a 10 nm gap, also known as the flying height, between the slider and the disk. In order to make the slider fly stably and reliably at such a small gap, various characteristics of the suspension design must be carefully designed, such as vertical stiffness (Kz), gimbal pitch and roll stiffness (Kp, Kr), and gimbal static attitude (pitch and roll static attitude (PSA and RSA respectively)).
The disk drive also typically includes a servo system that operates to move a slider or a head over a defined track on a disk surface. This operation is called a seeking operation. The performance or data transfer rate of the disk drive is a key performance characteristic. In order to achieve a higher performance/data transfer rate, seeking has become more aggressive, and is increasingly characterized by high speeds, high acceleration, and high deceleration. During the seek process, the slider flying height may change due to: (1) changes of airflow speed and direction; and (2) changes in suspension loads applied on the slider during acceleration and deceleration. The changes in suspension loads applied on the slider during acceleration and deceleration primarily occur due to the torque in the roll direction (for an in-line actuator). FIGS. 2a and 2b show examples of seeking acceleration and roll torque relative to seeking speed and as a function of time. For these examples, during the acceleration process, a negative roll torque is applied to the slider approximately at 0.5 ms. A positive roll torque change occurs during the deceleration process approximately at 6 ms. These roll torque changes may reduce the clearance between the slider and the disk, and may cause the slider to contact the disk, resulting in a drive failure. Therefore, the change in roll torque needs to be improved.
Changes in the roll torque may equal the acceleration or deceleration multiplied by the roll inertia moment. Conventionally, the roll torque may be reduced by reducing the acceleration or deceleration, but doing so may result in a negative effect on drive performance. Therefore, it is preferable to reduce the roll inertia moment instead. Further, during certain seek operations, the servo may lose control of the actuator, resulting in a loss of control over the acceleration or deceleration of the slider. In these situations, the actuator may slam into crash stops at the inner or outer diameters of the disk. During this process, the acceleration or deceleration of the slider may reach as high as ten times the normal seek operation acceleration or deceleration. Moreover, as a result of the loss of actuator control, the slider may contact the disk, resulting in severe damage to the disk and the slider. One solution for preventing damage to the disk was proposed in U.S. Pat. No. 6,125,017, issued to Misso et al., in which the crash stop was re-designed. Alternatively, another solution for preventing disk damage is to increase the breaking distance. This solution is not desirable as a larger braking distance directly reduces the disk area that can be used for data storage. Thus, it is even more preferable to reduce the roll inertia moment.
Thus, it would be desirable to have an improved head-gimbal assembly that reduces the roll inertia moment of a slider.